AVS 62nd International Symposium & Exhibition
    Thin Film Monday Sessions
       Session TF+AS+SS-MoM

Paper TF+AS+SS-MoM1
The Effects of Embedded Dipoles in Aromatic Self-Assembled Monolayers

Monday, October 19, 2015, 8:20 am, Room 111

Session: Self-Assembled Monolayers, Layer-by-Layer, etc.
Presenter: Swen Schuster, Universität Heidelberg, Germany
Authors: S. Schuster, Universität Heidelberg, Germany
T. Abu-Husein, Universität Frankfurt, Germany
D.A. Egger, Graz University of Technology, Austria
I. Hehn, Graz University of Technology, Austria
M. Kind, Universität Frankfurt, Germany
E. Zojer, Graz University of Technology, Austria
A. Terfort, Universität Frankfurt, Germany
M. Zharnikov, Universität Heidelberg, Germany
Correspondent: Click to Email
Self-assembled monolayers (SAMs) are frequently used as intermediate films to modify charge-carrier injection from metal-electrodes into an organic semiconductor. This is usually achieved by use of the terminal dipolar groups comprising the SAM-ambience interface and affecting, at the same time, the growth chemistry of the semiconductor. Here we suggest an alternative approach, viz. embedding dipolar element into the molecular backbone, which allows decoupling the dipole control and the interfacial chemistry. As molecular backbone we use oligophenyl moiety which provides a suitable structural match to most organic semiconductors. As polar unit we use pyrimidine, varying its orientation in the molecular backbone and, consequently, the direction of the embedded dipole moment. The electronic and structural properties of these embedded-dipole SAMs are thoroughly analyzed using a number of complementary characterization techniques combined with quantum-mechanical modeling. We show that such mid-chain substituted monolayers are highly interesting from both fundamental and application viewpoints, as the dipolar groups are found to induce a potential discontinuity inside the monolayer, electrostatically shifting the energy levels in the regions above and below the dipoles relative to one another. These SAMs also allow for tuning the substrate work function in a controlled manner independent of the docking and interfacial chemistry. In addition, a mixture of the embedded-dipole molecules with opposite orientations of dipoles makes possible a fine tuning of the work function between the ultimate values, associated with a particular dipole orientation. Quantum-mechanical modeling in conjunction with x-ray photoelectron spectroscopy experiments provides insight into the molecular organization of such mixed monolayers.